I have a problem in a web start application with java 7 and the new sort behavior (exception: comparison method violates its general contract).
So I like to go back to previous behavior and tried to put the new java 7 system property "java.util.Arrays.useLegacyMergeSort" in the generated jnlp-File:
<property name="java.util.Arrays.useLegacyMergeSort" value="true"/>.
Now I can read the property value in java code with System.getProperty("java.util.Arrays.useLegacyMergeSort"), and guess the property was successful set, but the exception still appears?!
The system property works with command line "javaws -J-Djava.util.Arrays.useLegacyMergeSort=true file.jnlp", but not via doubleclick on the jnlp-file or url and browser.
Only "trusted" set of properties can be set in the JNLP file by unsigned applications.
List of properties is revised from time to time but it usually takes time for new properties to be added to it (if there is strong demand for it as every property should undergo security audit).
You can specify arbitrary property if you sign your application and JNLP file.